Appraisal of metal contamination in sediments of lower reaches of Niger River, Nigeria, using contamination indices and sediment quality guidelines

ABSTRACT

Pollution of sediments by metals is a global issue, with developing countries like Nigeria, having its large PORTION. Niger River, the most valued river in Nigeria, is under serious anthropogenic perturbations with no measures to save the river by concerned authorities. Samplings were conducted at 12 designated stations of the lower reaches of the river within the southern region of Nigeria. The elements (As, Fe, Cu, Pb, Cd, Zn and Hg) were analysed using atomic absorption spectrophotometer. The average levels of As, Fe, Cu, Pb, Cd, Zn and Hg in the river sediments were 12, 115, 18, 11, 0.71, 36 and 0.59 mg/kg, respectively. Certain indices, including the enrichment factor (EF), geoaccumulation index (I_geo), pollution load index (PLI) and contamination factor (CF), were used to assess the ecological risk posed by metals in sediment. Cadmium in five locations (SP4− SP8) and Hg for sites SP4 and SP5, had their I_geo values above 1.0, which implies that these stations were moderately polluted. The EF values for Cd, Hg and As were above 1.5 (EF > 1.5) in sites SP4 and SP5 especially in the dry season, indicating strong enrichment of these elements in sediment to anthropogenic influences. Potential ecological risks of heavy metals in sediment showed weak to very high threat which implies that the condition is much frightening to the biota and inhabitants in the vicinity of the river as well.

KEYWORDS:

• Contamination indices
• effect range values
• Nigeria
• seasonal variation
• surface sediment

Acknowledgments

Our sincere appreciation goes to the Department of Zoology and Environmental Biology, University of Nigeria, Nsukka, for their thorough assessment and approval during the proposal stage of this work. The roles of fishermen in Anambra and Delta States, Nigeria, in providing the motorized boats used in sampling of the river and making available, rescue team in case of any mishap were highly appreciated.

Disclosure statement

The authors declare that they do not have known competing interests regarding the publication of this manuscript